Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

Doctors typically use weight, height and body-surface measurements to determine the proper doses of the powerful cancer-fighting drugs.

But many doctors avoid that approach with overweight breast cancer patients because they worry about the toxic side effects of very large doses, said Dr. Jennifer Griggs, the study’s lead author and a breast cancer specialist at the University of Rochester.

The phenomenon has been reported in treating other kinds of cancer.

Patients receiving lower doses
In her study of 9,672 women who received standard drugs for breast cancer, overweight women were 20 percent more likely than thin women to receive lower doses than a size-based formula would indicate they need; obese women were more than twice as likely; and very obese women were almost six times more likely.

Previous studies have suggested that overweight patients are more likely than lean ones to suffer a recurrence of their breast cancer, partly because excess fat increases the amount of circulating estrogen, which fuels the growth of some tumors.

Griggs said insufficient chemotherapy is probably also to blame. “It certainly seems like a plausible explanation,” she said.

Doctors worry about such side effects as fevers and a dangerous reduction in disease-fighting white blood cells. But relatively new drugs to boost white cell counts have probably helped ease those concerns, said Dr. Lydia Usha, a breast cancer specialist at Chicago’s Rush University Medical Center.

In Griggs’ study, 462 women were hospitalized for treatment of low white counts with fevers. The problem was not more common in overweight women who had received size-based doses.

Increased risk of complicationsChemotherapy also sometimes increases the risk of longer-term complications such as heart damage and other types of cancer — concerns that Usha said have led her to give obese patients lower doses than their size dictated.

The participants in the study were not followed long enough to compare long-term outcomes, but Griggs noted that a previous study found that overweight breast cancer patients given chemotherapy based on their size were as likely as lean women to survive without a recurrence.

Both studies raise concerns that doctors “are falsely thinking they’re making chemotherapy easier in them by giving them less,” but are actually doing obese women a disservice, said Dr. William Gradishar, a breast cancer specialist at Northwestern University.

Amgen Inc., a maker of white cell-boosting drugs, funded early data collection for Griggs’ research, and a co-author has served on an Amgen speakers’ bureau, but the researchers said the company had no role in the study design or analysis.